## Why learn about linear functions?

Joan loves to travel, but she doesn’t have a lot of extra spending cash. She read on several travel blogs that an awesome way to see the world is to get a credit card that offers an air mile bonus, and use it for all the things you normally budget for like food, gas, and even school supplies. This way, a big chunk of your airfare can be paid for with air miles.

She applied for and got a credit card with air miles. Joan has planned to use her air miles card for the following things each month:

• gas = $30 • car insurance =$40
• mobile phone bill = $65 • groceries =$150
• entertainment – restaurants, movies, and live music = \$50

Each dollar she spends gives her 1.25 air miles, and she expects to need about 12,000 air miles to buy the ticket she wants. Joan would like to plan how long she needs to save so that she’ll know when to start looking for a good deal on airfare, but she isn’t sure how to make sense of all the details of her budget and airfare needs.

In this module, you will learn how to take information like Joan’s and translate it into mathematical functions that can help answer questions like, “how long do I need to save for a trip?” We will revisit Joan at the end of this module and help her figure out how long she will need to use her air miles card before she has enough air miles for her trip.